1. Technical Field
The present invention relates to an apparatus for sheeting dough products and, in particular, to a series of ultrasonic horns or blades used to strip a sheeter roller. The use of ultrasonic horns eliminates the need for a stripper wire and allows for the production of full-width dough sheets.
2. Description of Related Art
A sheeter is a device commonly used in the food industry for making flattened food products, such as tortilla chips, in a continuous processing operation. Typically, a dough product is compressed between a pair of counter rotating sheeter rollers that are located closely together, thereby providing a pinch point through which the dough is formed into sheets. The dough can then be cut by, for example, a cutting roller to form the shape of the product desired.
Many dough products, particularly those that are corn based (xe2x80x9cmasaxe2x80x9d), have a tendency to stick to the sheeter rollers rather than dropping onto a conveyer for transportation to the next processing step, such as a baking oven. This is because masa is relatively sticky and has very little cohesive strength. The masa will not support its weight as it falls from the sheeter and cannot be pulled off the sheeter. The use of a stationary scraper blade, as is commonly used with flour dough applications, is not practical because the masa tends to build on and stick to the scraper blade. One common approach to this problem is to string a stripper wire across the face of the sheeter roller so that the stripper wire can scrap away the dough product off of the surface of the roller.
An example of a prior art sheeter wire design in this regard is illustrated by FIGS. 1 and 2. FIG. 1 is a perspective view of the output of a dough sheeter device 110. The cut dough product, in this case uncooked tortilla chips 120 made from masa, can be seen on a conveyer 130 after being deposited on the conveyer 130 by a sheeter roller 140. The sheeter roller 140 will typically have a plurality of plastic bands 150 about the circumference of the sheeter roller 140. These bands 150 ride in groves (now shown) in the sheeter roller 140 and hold the sheeter wire 160 close to the surface of the sheeter roller 140. The bands 150 also provide a surface for returning ribbons of unused masa to the sheeter 110.
A sheeter wire 160 is shown strung across the face of the sheeter roller 140. This sheeter wire 160 is attached to two fixed points 170, 180 and is threaded across the face of the sheeter roller 140 underneath each of the bands 150. This provides a flush contact between the sheeter wire 160 and the surface of the sheeter roller 140. The second fixed point 180 could also comprise a tension device such as a hydraulic or pneumatic device that provides a constant tension on the wire 160. Such a tension device is typically connected to a warning device to provide an indication of wire breakage.
FIG. 2 is a schematic side view of a prior art sheeter wire design installed on a sheeter device. Masa 205 is fed between a press roller 207 and the sheeter roller 240. The press roller 207 turns at a slower rotational speed than the sheeter roller 240. This results in the masa 205 adhering to the sheeter roller 240. The masa 205 is next cut by a cutter roller 209. The cut masa is then stripped from the sheeter roller 240, by the sheeter wire 260. The cut product 220 then drops onto a conveyor 230 to be transported for further processing. As will be described below, sheeters using a sheeter wire arrangement such as illustrated in FIGS. 1 and 2 have three primary drawbacksxe2x80x94wire 160 breakage, band 150 breakage, and an inability to produce full-width sheets.
Returning to FIG. 1, the sheeter wire 160 is typically commercial piano wire. A typical tension on the wire during operation is 100 to 125 pounds. Contact with hardened masa, particularly during start-up, can subject the sheeter wire 160 to higher tension for short time periods. During operation the wire 160 is also subject to friction from the moving face of the sheeter roller 140. This wire 160 must be replaced periodically or the wire 160 is prone to breakage after time. In fact, in a continuous use operation for a typical sheeter device producing tortilla chips, it has been observed that such fixed sheeter wire 160 will break, if not replaced, nearly daily.
In order to replace a broken sheeter wire the entire sheeter device 110 and, consequently, the entire chip processing assembly, must be stopped. The broken sheeter wire 160 is removed. A new sheeter wire 160 is attached to the first attaching point 170, strung across the face of the sheeter roller 140 under the bands 150, and attached to a second attaching point 180. Then the tension device 190 must be reactivated. Raw material is lost because the dough that was on the sheeter must be thrown away and additional product downstream may need to be discarded. Start-up procedures must next be followed, which result in further lost product. A wire breakage event, therefore, results in a substantial amount of unscheduled downtime and lost product. The alternative is to schedule, on a daily basis, the replacement of the sheeter wire 160. A scheduled replacement of the sheeter wire 160, however, results in even more frequent, although scheduled, downtime.
One attempt at addressing the wire breakage problem is reflected in U.S. Pat. No. 5,720,990 (xe2x80x9cLawrencexe2x80x9d) issued on Feb. 24, 1998. The Lawrence patent discloses a wire separator system for a sheeter device comprising a motor that drives a feed spool and a motor that drives a take-up spool. Tension is maintained on the sheeter wire by use of a tension sensing pulley providing input to a controller which modulates the torque on the take-up reel. Provided that the wire does not unexpectedly break, the Lawrence patent discloses a device that will allow the sheeter to run for long periods of time without the necessity of stopping the sheeter to replace the sheeter wire, because new wire is constantly drawn across the contact surface.
The invention disclosed by Lawrence has several drawbacks, however. First, the design assumes that the wire will not break during operation. Unfortunately, this is not a safe assumption. In fact, it is not an infrequent occurrence that wire breakage occurs on the prior art model illustrated by FIG. 1 shortly after a new wire has been installed. This could occur due to a sudden contact with a dried piece of dough that has become affixed to the sheeter while the sheeter is stationary. Further, an initial steady-state friction between the sheeter wire and the sheeter must be overcome at the instant the sheeter begins to rotate. Since the Lawrence device provides that one motor feeds wire while another motor takes-up wire, a breakage between the two motors can result in the continued feeding of wire into the sheeter until the feed motor comes to a stop. A breakage also results in a loss of tension on the feed spool and can lead to unraveling or the xe2x80x9cweed eaterxe2x80x9d effect, whereby the spool becomes unwound. Further, the Lawrence device is designed to maintain constant tension of the wire by using a variable speed pulling motor connected to the take-up reel. Since the Lawrence feed spool is connected to a fixed speed motor, the tension will necessarily fluctuate at the point that the wire is leaving the feed spool when, for example, the wire encounters a piece of dried dough product on the sheeter during operation. These torque fluctuations could effect the consistency of the feed spool""s wound tension, thereby leading to further torque fluctuations and potential feed problems.
Minor breakage issues aside, the prior art sheeter device illustrated in FIG. 1 and the Lawrence device have other shortcomings and problems. For example, the bands 150 that hold the sheeter wire 160 in place are also subject to frequent breakage. Band breakage will probably occur with even greater frequency when a continuously drawn sheeter wire 160, such as disclosed in Lawrence, is used. Again, as with a wire 160 breakage event, band 150 breakage results in stopping the entire sheeter device and assembly line, thereby resulting in down time, loss of downstream product, and loss of product due to start-up procedure requirements. These bands can be periodically replaced; however, replacement also requires shutting down the sheeter device.
The use of bands 150 also precludes the possibility of sheeting a fall-width sheet of dough product. This is because masa adheres to the exterior of the bands 150 and is returned in ribbons to the sheeter 110. It may be desirable in certain applications to sheet an uncut, full-width continuous sheet of masa. For example, it may be desirable to cook or partially cook the sheet of dough downstream from the sheeter and then later apply a die cutter to the sheet. Such an arrangement would allow for a higher volume of product to be dispensed from a single sheeter since little to no dough is returned to the sheeter.
Consequently, a need exists for a dough sheeting device capable of sheeting masa and other sticky dough products without the use of stripper wire and the attending bands. Such apparatus should be capable of producing a full-width and continuous sheet of masa without a buildup of masa on the stripping mechanism.
The proposed invention comprises a sheeter device that utilizes a series of vibrating horns in close proximity to the sheeter roller for stripping the sheeted product off the roller, thereby forming a fall-width continuous sheet of dough. The horns vibrate in the ultrasonic range, thereby precluding masa buildup on the surface of the horns.
Use of the ultrasonic horns as a scraping device eliminates the need for a sheer wire and the attending bands. Consequently, the invention can be operated continuously without concern for replacing worn or broken sheeter wire or bands. Further, since the need for bands is eliminated, the device can produce fall-width, continuous sheets of dough product. These full-width sheets result in a higher volume of dough product being produced by a single sheeter device. This is evident by the fact that dough does not return to the sheeter as ribbons attached to the bands.
The above as well as additional features and advantages of the present invention will become apparent in the following written detailed description.